This invention relates to a wiring-connecting material making use of an adhesive composition and conductive particles, and a process for producing a wiring-connected board.
Epoxy resin adhesives are widely used for various purposes such as electric, electronic, construction, automobile and airplane materials because they can provide a high bond strength and have excellent resistance to water and resistance to heat. In particular, one-pack type epoxy resin adhesives are usable with ease because it is unnecessary to blend the chief material and the curing agent, and are widely used in the form of film, paste or powder. In such one-pack type epoxy resin adhesive, epoxy resins, curing agents and modifiers can be combined in variety. Hence, appropriate selection of their combination enables achievement of any desired performance as disclosed in, e.g., Japanese Patent Application Laid-open (KOKAI) No. Sho62-141083.
A filmlike adhesive disclosed in this Japanese Patent Application Laid-open (KOKAI) No. Sho62-141083, however, can not sufficiently be reactive at the time of curing because it uses a catalytic curing agent which is inert at normal temperature, in order to achieve both short-time curing properties (fast-curing performance) and storage stability (storage properties) to attain a good stability. Thus, though having a good operability, it must be heated at about 140xc2x0 C. to about 180xc2x0 C. for a connecting time of about 20 seconds, or must be heated at about 180xc2x0 C. to about 210xc2x0 C. for a connecting time of 10 seconds.
In recent years, however, in the field of precision electronic instruments, circuits are being made highly dense, so that connecting terminals have come to be formed in and at very narrow width and pitch. Hence, this has caused come-off or peeling and misregistration of wiring in some cases when terminals are interconnected under connecting conditions adapted to such conventional epoxy resin wiring-connecting materials. Also, it has been sought to shorten connecting time so as to enable connection within 10 seconds in order to improve production efficiency. To satisfy these demands, it is sought to provide a low-temperature fast-curable wiring-connecting material capable of curing at a low temperature and yet in a short time.
An object of the present invention is to provide a wiring-connecting material for electric and electronic use, having better low-temperature fast-curing performance than any conventional epoxy resin connecting materials and also having a pot life, and a process for producing a wiring-connected board making use of such a connecting material.
The present invention provides a wiring-connecting material comprising from2 to 75 parts by weight of a polyurethane resin, from 30 to 60 parts by weight of a radical-polymerizable substance and from 0.1 to 30 parts by weight of a curing agent generating a free radical upon heating. The wiring-connecting material of the present invention is especially preferable as a connecting material which is interposed between connecting terminals facing each other and with which the connecting terminals are electrically interconnected in the pressure direction while pressing the connecting terminals facing each other.
The wiring-connecting material of the present invention may also preferably further comprise a film-forming material and/or conductive particles. The film-forming material may preferably be mixed in an amount of from 0 to 40 parts by weight, and a polyimide resin is preferred.
As the polyurethane resin, a resin having a flow point of from 40xc2x0 C. to 140xc2x0 C. as measured by the flow tester method may preferably be used. As the curing agent, it is preferable to use a curing agent having a weight retention at 25xc2x0 C. for 24 hours (i.e., the proportion of a difference in mass before and after open-leaving at room temperature (25xc2x0 C.) and normal pressure for 24 hours, with respect to the mass before leaving) of not less than 20% by weight. As the radical-polymerizable substance, urethane acrylate is preferred.
The present invention also provides a wiring-connected board production process comprising the step of interconnecting terminals of wiring by the use of the wiring-connecting material of the present invention. More specifically, the present invention provides a process for producing a wiring-connected board, comprising a connecting step of interconnecting wiring members each having a connecting terminal, which members are so interconnected that their connecting terminals are able to make conduction between them;
the connecting step comprising the step of heating the wiring-connecting material of the present invention while applying a pressure thereto via the wiring members; the wiring-connecting material being held between at least two wiring members so disposed that their sides having the connecting terminals face to each other. This production process of the present invention is especially preferable when at least one surface of the connecting terminal is formed of at least one metal selected from gold, silver and a platinum group metal.